Testing apparatus



Sept. 15, 1925. 1,553,465

H. s. OSBORNE 'rss'rme APPARATUS Filed Aug, 9. 1920 T Y V INVENTOR 7ATTORNEY Patent ed Sept. 15, 1925.

UNITED. STATES HAROLD s. OSBORNE, on NEW YORK, N. Y.,

ASSIGNOR To AMERICAN TELErHonE AND TELEGRAPH COMPANY, A CORPORATION OFNEW YORK.

TESTING APPARATUS.

Application filed August 9, 1920. Serial No. 402,238.

The'term unbalance as employed hereindesignates an unsymmetricalcondition of the wires of a circuit with respect to adjacent wires or toground, which unbalance gives rise to cross-talk or noise in theunbalanced circuit, as is well known to those familiar with the art. Theunbalance may be .due to any number of causes, such as high resistancejoints in the line wires, defective loading coils, transpositionirregularities, broken insulators and various other 25 circumstances.

The present invention proposes means whereby the existence of imbalancesof this character may be rapidly determined. The magnitude of the effectof the unbalance in causing noise and cross-talk in telephoneinstruments associated with the line may also be ascertained so that thetesting operator is enabled to determine whether or not the unbalance isof such nature that its location should be ascertained and the causethereof removed.

A good understanding of the invention may be had from the followingdescription thereof, reference being had to the accompanying drawing, inwhich,

Figure 1 is. a diagrammatic view showing one form of embodiment of theinvention, and

Fig. 2 is a similar view showing one form of measuring device for usewith the apparatus of Fig. 1.

Similar characters of reference designate similar parts in each oftheviews.

In Fig. 1 of the drawing reference charac ter L, designates thetransmission line, the unbalance of which is to be ascertained. S is afrequency band oscillator covering substantially the range of the voice,which 05 'for current from S.

cillator may be associated with the line L adjacent its western terminalby means of a 65 switch 1 connected to the midpoint of the winding of atransformer T. At its eastern end, the line is terminated by means of atransformer V, the midpoint of which is associated with a switch 2,which in the posi-- tion shown in the drawing, makes contact with oneterminal of an impedance Z, the other terminal" of which is connected toground. With switches 1 and 2 in their left-and right positionsrespectively, current from the oscillator flows over the sides ofcircuit L in parallel through'impedance Z, to ground return. Thiscircuit, it will be observed, is a grounded phantom and the impedance Zis provided to so terminate the eastern end of the line that reflectionlosses in the phantom circuit are substantially eliminated. Thisimpedance is herein illustrated as composed of a simple resistance, butit may consist of a combination of impedance elements where greateraccuracy of termination is desired. An oscillator S similar to S, isprovided at the e'ast-ernter- 'minal of the line for at times causingflow of current from east to west, and an 'impedanoe Z is provided atthe western end of the line to properly terminate the same Currentmeasuring instruments, M and M are associated with the secondarywindings of transformers T 35 and V.

If the line'is in perfect balance, the impedance of one side of the lineis equal to that of the other, so that current applied thereto by Sor Sdivides equally and traverses the windings of transformers T andV inopposite directions, so that the measuring instruments M and M show zerocurrent. However, if an unbalance is present, such as the seriesinductance indicated in dotted lines at the point X, the dropofpotential across'this unbalance causes a flow of current whichcirculates in the circuit composed of the lin'ec'onductors inseries-with each other and the windings of the transformers T and V. Themeasuring instruments, therefore, show a current, the value of which. isdependent upon the magnitude of the unbalance, the location thereof,andthe direction of flow of the phantom current.

A Supp se, for illustration, that the unbalits ance X is close to thewestern terminal of the line, then in case (a) current is applied to theline by the source S, the measuring instrument M will indicate a muchlarger value of current than M for the reason that the circulatingcurrent has substantially its full value at the western terminal of theline, whereas, when it reaches the eastern end it has been decreased invalue owing to the attenuation of the metallic circuit. However, in case(7)) current is applied to the line by source S the indication of theinstrument M is very small, owing to the fact that the rents.

circulating current is reduced in amplitude owing to the attenuation ofthe metallic circuit. The indication of the instrument M in case (a) islarger than that of M in case (b) for the reason that the circulatingcurrent is substantially unattenuated in the former case; The readingsof M in case (w) and M in case (Z9) serve to give an approximateindication of the location of the unbalance.

The reading of M in case (0,) and M in case- (b) are of the same orderof magnitude, provided the attenuation of the metallic circuit issubstantially equal to that of the grounded circuit. In other words, thelocation of the unbalance does not have any pronounced effect on thesaid readings. The last mentioned measurements are therefore of servicein arriving at an estimate of the quality of the line from thestandpoint of balance. If the readings are below a predeterminedmaximum, the line may be regardedas in good condition and if it exceedssaid value, steps must be taken to remove the irregularities which causethe unbalance. v

The devices M and M may be any suit-- able instruments for measuringweak cur- They may, for example, each consist of the arrangement, shownin Fig. 2, in which R is a telephone receiver which is normallyassociated with the secondary of transformer T by means of the contactsprings of the key K.

The source S is associated with the line by another spring of the keyand the switch 1.

The circulating current caused in the line by the current from S flowsthrough transformer T and causes a response of receiver R.

The test-operator now reverses the key, thus connecting S to thevariable impedance device V and the receiver R to the movable contact 4,so that part of the current in V enters the receiver. He varies theposition of contact 4 until the sound in the receiver has the sameloudness for either position of switch K. He then reads a scaleassociated with the contact 4:, which scale is calibrated in anyconvenient units. The impedance of the device V is arranged to be thesame as that of the phantom circuit over the line L, so that the currentflowing from S is the same for either position of the key. The

position of contact 4 consequently shows the fraction of the totalcurrent from S which is caused to circulate in the line-owing toirregularities. The impedance of the receiver circuit is made so highthat the variation in the position of contact 4 has no appreciableeffect on the impedance of V. If the phantom current is applied to theline at its other end, the operator throws switch 1 into its otherposition, and determines the value of the circulating current in thesame manner.

Although only one form of apparatus and circuits embodying the inventionand only one form of method of practicing the same are described herein,it is readily understood that various changes and modifications may bemade therein within the scope of the following claims without departingfrom the spirit and scope of the invention.

What is claimed is:

1. The method of testing a transmission circuit for unbalances of thecharacter described, which consists in associating with one end of theconductors of the line in parallel with each other a source of currentand measuring the current flowing from one conductor of the line to theother at 3. The method of arriving at a rough approximation of thelocation of an unbalance of the nature described, which consists inassociating current of a plurality of frequencies, first with one end ofthe conductors of the line in parallel with each other, and then withthe other, and measuring for each case the current flowing from oneconductor to the other at the same end of the conductors.

4. In an apparatus for testing a transmission circuit for unbalances ofthe nature described, a source of current and connections associatedtherewith for causing How of current through the conductors of thecircuit in parallel with each other, and a measuring instrument fordetermining at the distant end of said circuit the flow of current fromthe conductor of one side into the conductor of the other side.

5. In an apparatus for testing a transapparatus being responsive only tocurrent circulating in said conductors in series with each other.

6. In an apparatus for testing a transmission line for unbalances of thenature described, a plurality of sources of current, each source havinga plurality of frequencies, connecting devices for associating one orthe other of said sources with said line to cause flow of current in onedirection or the other over said conductors thereof in parallel witheach other, impedance devices for terminating the line at the end remotefrom vtlre source associated therewith to reduce reflection lossesthereat, and measuring apparatus associated with the terminals of saidline and responsive to current circulating in said conductors in serieswith each other, but nonresponsive to current traversing said conductorsin parallel with each other.

7. The method of testing a transmission circuit for unbalance betweenits two conductors, which consists in connecting a source of current tosaid conductors in parallel, and measuring the current flow across saidconductors at their distant end.

'8. The method of testing a transmission circuit for unbalance betweenits two conductors, which consists in connecting a source of current atone end to said conductors in parallel, and measuring the current flowacross said conductors at both the near and distant ends thereof.

9. The method of locating a cause or unbalance between the twoconductors of a transmission circuit, which consists in applying asource of current at one end through said conductors in parallel,measuring the current flow across said conductors at both the near anddistant ends thereof, and thereby getting an indication of the locationof said cause by the relative magnitudes of the said currents across theends In testimony whereof, I have signed 111 name to this specificationthis 5th day of August 1920.

HAROLD S. OSBORNE.

